This invention relates to ambient air catalytic oxidation of saturated hydrocarbons, specifically to efficient catalytic oxidative conversion of hydrocarbons to aldehydes and unsaturated alcohols employing catalysts based on molecular strings of di-, tri- and/or poly-groups of bonded transition metal complexes.
A number of chemical reaction paths have previously been investigated for single step conversion of aliphatic hydrocarbons to aldehydes or alcohols but none teach high conversion efficiencies without employment of high temperature and pressure, aggressive chemical oxidizers or strong chemical agents. For example, controlled oxidation of methane, investigated under a wide range of conditions, has produced carbon dioxide, carbon monoxide, low concentrations of unsaturated hydrocarbons, oligomers, low levels of alcohols, aldehydes and water. None of these efforts have produced significant amounts of aldehydes or alcohols. As a result direct conversion of saturated hydrocarbons to aldehydes and/or alcohols has essentially been abandoned in favor of conversion of more labile hydrocarbons such as alkenes or other organic compounds with reactive groups. The invention disclosed in this application teaches catalytic air oxidative conversion of aliphatic hydrocarbons directly to aldehydes and unsaturated alcohols at room temperature and above using di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts without addition of aggressive chemical oxidizing agents and without addition of other strong chemicals. No labile or other reactive chemical groups are required for production of aldehydes and unsaturated alcohols from saturated hydrocarbons. Use of di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts described in this application produce a significantly higher yield of oxidized products than the relatively inactive mono-metal transition metal compounds.
Air oxidation of hydrocarbon vapors has been accomplished in pressurized reactions at elevated temperatures in the presence of selected transition metal salts or on the surface of shaped pore solid zeolites. Olefin or alkenyl type unsaturated hydrocarbons may be oxidized to aldehydes with air or oxygen at elevated temperatures in the presence of transition metal compounds as taught in the following patents. U.S. Pat. No. 6,143,928, issued Nov. 7, 2000, teaches of the catalytic oxidation of propylene with molecular oxygen containing gas at 100xc2x0 C. to 450xc2x0 C. and 1 to 50 bars pressure. U.S. Pat. No. 6,069,282, issued May 30, 2000, discloses preparation of vinyl, alkynyl or aryl aldehydes by reaction of vinyl, alkynyl or aryl-methanols with the aid of a mediator and an oxidant, wherein the mediator is selected from the group of aliphatic, cycloalphatic, heterocyclic or aromatic NO or NOH containing compounds. U.S. Pat. No. 5,426,238, issued Jun. 20, 1995, introduces a method for producing an aldehyde, which comprises reacting an olefin with carbon monoxide and hydrogen in a hydroformulation reaction in the presence of a rhodium catalyst with an organophosphorus ligand. U.S. Pat. No. 5,409,877, issued Apr. 25, 1995, demonstrates another method for production of an aldehyde and an alcohol using a heterogeneous transition metal catalyst for the hydroformylation of an olefin with H2 and CO. These disclosures employ the labile olefinic double bond as a reaction site for selective oxidation but do not describe a method for convenient conversion of saturated hydrocarbons to aldehydes.
Strong chemical oxidizing agents have also been employed for controlled oxidative conversion of alcohols, alkenes and other labile compounds to aldehydes and other products under controlled conditions. U.S. Pat. No. 5,698,744, issued Dec. 16, 1997, shows a process for the selective oxidation employing ferromagnetic chromium dioxide. U.S. Pat. No. 5,602,280, issued Feb. 11, 1997, formed an unsaturated aldehyde and an unsaturated carboxylic acid by subjecting propylene, isobutylene or tertiary butanol to gas phase catalytic oxidation with molecular oxygen in the presence of transition metal oxides including tungsten oxides followed by re-oxidation of the transition metal oxide to its original oxidation state. Here the metal oxides may be considered to be co-reactants since they require re-oxidation by oxygen gas to be converted back to their beginning state. U.S. Pat. No. 4,885,412, issued Dec. 5, 1989, teaches a process for producing an aldehyde from alkylaromatics in the vapor phase in the presence of molten nitrate salt catalysts. Here the term catalyst has been used to indicate the necessity for a chemical oxidizer in the form of a molten nitrate. U.S. Pat. No. 4,859,799, issued Aug. 22, 1989, introduced a process for production of aldehydes or ketones by oxidative cleavage of olefinic double bonds by means of a coordination complex of a ligand and a peroxo derivative of a transition metal. Even electrochemical techniques have been employed to drive oxidative reactions of organic compounds as described in U.S. Pat. No. 4,387,007, issued Jun. 7, 1983, in which para-tertiary-butylbenzaldehyde was manufactured by the electrochemical oxidation of para-tertiary-butyltoluene. These chemical reactions required the oxidizing power of strong chemical oxidizing agents or electrochemistry to achieve product aldehydes.
Strong chemicals such as strong acids and strong base hydroxides have also been used to achieve conversion of labile compounds to aldehydes. U.S. Pat. No. 4,562,297, issued Dec. 31, 1985, teaches that 3,5-dihydrocarbyl-4-hydroxybenzaldehydes are prepared from 4-(1-alkyenyl)-2,5-dihydrocarbylphenol, such as 1,1-dimethyl-2-(3,5-di-ter-t-butyl-4-hydroxyphenyl)ethene, with at least a stoichiometric amount of an oxygen-containing gas at 50xc2x0 C. to 250xc2x0 C. in the presence of an alcohol solvent and a catalytic amount of an alkali or alkaline earth metal hydroxide. U.S. Pat. No. 4,240,985, issued Dec. 23, 1980, produced aldehydes by cleaving 2,2-dialkyltetrahydropyrans bearing two hydrogen atoms in the sixth position using a strong acid. Thus, it is apparent that there are three classes of existing processes for preparation of aldehydes with mono-transition metal compounds: one class converts labile groups, including unsaturated or olefinic compounds with or without hydrogen, alcohols and other labile groups to aldehydes by chemical conversion. A second process class employs strong chemical oxidizing agents, such as permanganates, chromates, perchlorates, peroxides, chromium oxides and other oxygen rich chemical agents at elevated temperature to produce aldehydes. A third class of processes uses strong acids or strong bases to affect chemical conversion in the production of selected aldehydes. None of these patents teach how to convert saturated hydrocarbons to aldehydes at ambient conditions.
Olefins or unsaturated hydrocarbons can also be oxidized to alcohols with oxygen or by strong chemical means, usually at elevated temperatures and pressures, in the presence or absence of transition metal compounds. U.S. Pat. No. 5,623,090 issued Apr. 22, 1997, U.S. Pat. No. 5,414,145 issued May 9, 1995 and U.S. Pat. No. 4,296,262 issued Oct. 20, 1981 oxidized olefins with oxygen to form alcohols, while U.S. patent issued Aug. 30, 1977 and U.S. Pat. No. 4,013,729 issued Mar. 22, 1977 oxidized olefins by strong chemical means. Olefins can also be hydrolyzed to produce alcohols as taught in U.S. Pat. No. 4,956,506 issued Sep. 11, 1990, U.S. Pat. No. 4,857,664 issued Aug. 15, 1989, U.S. Pat. No. 4,484,013 issued Nov. 20, 1984, U.S. Pat. No. 4,476,333 issued Oct. 9, 1984, U.S. Pat. No. 4,469,903 issued Sep. 4, 1984, U.S. Pat. No. 4,456,776 issued Jun. 26, 1984, U.S. Pat. No. 4,408,085 issued Oct. 4, 1983, U.S. Pat. No. 4,360,406 issued Nov. 23, 1982, U.S. Pat. No. 4,306,084 issued Dec. 15, 1981, U.S. Pat. No. 4,296,263 issued Oct. 20, 1981, U.S. Pat. No. 4,270,011 issued May 26, 1981 and U.S. Pat. No. 4,180,688 issued Dec 25, 1979.
Carbonylation has been invoked under various conditions for the production of alcohols as in U.S. Pat. No. 4,956,392 issued Sep. 11, 1990, U.S. Pat. No. 4,607,055 issued Aug. 19, 1986, U.S. Pat. No. 4,560,672 issued Dec. 24, 1985, U.S. Pat. No. 4,551,444 issued Nov. 5, 1985, U.S. Pat. No. 4,537,909 issued Aug. 27, 1985, U.S. Pat. No. 4,144,401 issued Mar. 13, 1979 and U.S. Pat. No. 4,072,720 issued Feb. 7, 1978.
Hydrocarbons have also been chemically oxidized forming peroxides which were subsequently converted to alcohols as shown in U.S. Pat. No. 4,910,349 issued Mar. 20, 1990, U.S. Pat. No. 4,910,349 issued Mar. 20, 1990, U.S. Pat. No. 4,112,004 issued Sep. 5, 1978 and U.S. Pat. No. 4,065,511 issued Dec. 27, 1977. Thus, it is apparent that many of the processes employed for the production of aldehydes have also been modified for the production of alcohols. None of these patents teach direct oxidative conversion of saturated aliphatic hydrocarbon to aldehydes and unsaturated alcohols without use of aggressive chemical oxidizing agents or other strong chemical means.
Formaldehyde has been formed in low yields by oxidizing methane with oxygen or by strong chemical means, usually at elevated temperatures and pressures, in the presence of transition metal compounds. U.S. Pat. No. 5,856,585 issued Jan. 5, 1999, U.S. Pat. No. 4,705,771 issued Nov. 10, 1987 and U.S. Pat. No. 3,996,294 issued Dec. 7, 1976 oxidized methane with oxygen to form formaldehyde in yields of less than ten percent.
Methanol has been dehydrogenated under various conditions in the gas phase for the production of formaldehyde as in U.S. Pat. No. 6,147,263 issued Nov. 14, 2000, U.S. Pat. No. 5,990,358 issued Nov. 23, 1999, U.S. Pat. No. 4,544,773 issued Oct. 1, 1985, U.S. Pat. No. 4,474,996 issued Oct. 2, 1984, U.S. Pat. No. 4,454,354 issued Jun. 12 and 1984, U.S. Pat. No. 4,450,301 issued May 22, 1984. These patents invoke labile hydrocarbons for production of formaldehyde as opposed to starting with aliphatic hydrocarbons.
The invention disclosed in this application is different from the classifications referenced above in that aliphatic hydrocarbons are catalytically, directly air oxidized at room temperature and above using di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts without addition of aggressive chemical oxidizing agents and without addition of other strong chemicals. In addition, hydrocarbons can be oxidized with equal molar amounts of air to form aldehydes in high yields. No labile or other reactive chemical groups are required for production of aldehydes and unsaturated alcohols from saturated hydrocarbons.
Direct air oxidation catalysts of the di-metal, tri-metal and/or poly-metal backbone type, employed in the title invention, have facilitated oxidation processes of hydrocarbons at ambient conditions wherein aldehydes and unsaturated alcohols products were formed while mono-metal compounds were ineffective. For example, a process comprising a stirred aqueous mixture containing 14,000 ppm n-decane at a temperature of 16xc2x0 C. was oxidized in air, using an [iron(II)]2 catalyst thereby reducing the n-decane reactant to a concentration of  less than 900 ppm in five hours. Furthermore, a stirred aqueous mixture containing hexanes at ambient temperature was oxidized in air using related catalysts thereby reducing the concentration in a similar fashion. These same molecular string catalysts are also effective in oxidizing gasoline and diesel fuel in soil at ambient conditions. For example, 100 mg/kg of gasoline and 100 mg/kg of diesel fuel in soil have been air oxidized in 15 to 20 days reducing the hydrocarbon concentrations to less than 1 mg/kg forming aldehydes and other products. This ambient temperature air oxidation of hydrocarbons can be of value in eliminating such spilled hydrocarbons from a chemically sensitive environment. In addition, methane gas has been catalytically oxidized to formaldehyde and water vapor in yields in excess of 90 percent at elevated temperatures over a [cobalt(II)]3 catalyst. In each case use of the respective mono-metal catalyst produced no detectable oxidized products.
Selective use of different di-, tri- and/or poly-groups of transition metal catalysts are employed in the catalytic process for production of mono-and di-aldehydes and unsaturated alcohols. For example, primary and secondary aliphatic hydrocarbons, and such aliphatic groups that may be attached to alkenes, aromatics and other non-aliphatic moieties, can be catalytically air oxidized to convert the hydrocarbon or alkyl groups to aldehydes. Similarly, tertiary aliphatic hydrocarbons can be catalytically air oxidized to convert the hydrocarbon or alkyl groups to alcohols. Similarly, methane has been oxidatively converted to formaldehyde by this same process.
It is an object of this invention, therefore, to provide a molecular string type transition metal catalytic process for air oxidative conversion of aliphatic hydrocarbons, and alkyl groups attached to other compounds, to aldehydes and unsaturated alcohols.
It is another object of this invention to provide molecular string type catalysts for direct ambient air oxidation of hydrocarbons including hexanes, octanes, decanes, hydrocarbon oils, solvents, gasoline, jet fuel, diesel fuel, heating and lubricating oils, mineral spirits and other solvent type hydrocarbons.
It is another object of this invention to provide a molecular string type catalytic process for direct oxidative conversion of hydrocarbon reactants to aldehydes and unsaturated alcohol products without use of aggressive chemical oxidizing agents or other strong chemicals. Other objects of this invention will be apparent from the detailed description thereof which follows, and from the claims.
This invention describes a chemical process using any member of a family of transition metal catalysts, based on a di-metal, tri-metal and/or poly-metal backbone or string, for oxidation of aliphatic hydrocarbons at ambient temperature and above producing aldehydes and unsaturated alcohols. These catalysts have been effectively demonstrated to be active for oxidation of linear and branched hydrocarbons.
The process for catalytic oxidation of hydrocarbons to aldehydes and unsaturated alcohols in high yields is based on catalysts possessing multiple metal type transition metal compounds, such as [iron]2 or [manganese]2 type compounds. These catalysts have been designed based on a formal theory of catalysis, and the catalysts have been produced, and tested to prove their activity. The theory of catalysis rests upon a requirement that a catalyst possess a linear backbone or molecular string such that transitions from one molecular electronic configuration to another be essentially barrier free so reactants may proceed freely to products. Catalysts effective for ambient air oxidation of hydrocarbons can be made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of the transition metals, comprising titanium, manganese, iron, cobalt, nickel, copper, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof These catalysts are made in the absence of oxygen so as to produce compounds in the divalent state or other low oxidation state. Anions employed for these catalysts comprise chloride, bromide, cyanide, isocyanate, thiocyanate, metal cyanides, sulfate, phosphate, oxide, oxalate and other more complex groups, only some of which are found to be non-toxic to the natural environment. Mixed transition metal compounds have also been found to be effective catalysts for ambient air oxidation of organic compounds. For example, compounds containing a iron(II).copper(I) backbone or bond are also effective for oxidization of hydrocarbons using ambient air.
Numerous different Cu.Fe, [iron]2, [iron]3, [manganese]2 and related oxidation catalysts have been prepared for air oxidation of n-decane in water at ambient pressure and at a temperature of 0xc2x0 C. and above. These same catalysts were effective for oxidation of 20 ppm gasoline, 100 ppm diesel fuel, 200 ppm hexanes and pure n-decane in water with use of atmospheric air. Oxidation reactions can be conducted in ambient air at room temperature in an open top stirred container converting the hydrocarbons to aldehydes in yields in excess of seventy percent. In addition, several [iron]2 catalysts have proven to be efficient for complete oxidation of gasoline and/or diesel fuel in soil. Vapor phase reactions have been conducted at elevated temperature using a tube type reactor and [cobalt]3 catalysts for ambient air oxidative conversion of methane to formaldehyde in yields in excess of ninety percent based on methane.
Catalyst Selection Considerations
The fundamentals of catalysis effort forms a basis for selecting molecular catalysts for specified chemical reactions through computational methods by means of the following six process steps. An acceptable oxidation mechanism, involving two sets of pairs of metal atoms, was established for oxygen gas in the presence of water (step 1). A specific transition metal, such as iron, was selected as a possible catalytic site as found in an Mxe2x80x94M or Fexe2x80x94Fe string (step 2), bonded with four oxygen molecules in a D4h point group symmetry configuration, and having a computed bonding energy to the associated oxygen reactants of less than xe2x88x9260 kcal/mol (step 3). The first valence state for which the energy values were two-fold degenerate was 2+ (step 4). Cyanide, chloride and other anions may be chosen provided they are chemically compatible with the metal, M (Fe), in formation of the catalyst (step 5). A test should also be conducted to establish compliance with the rule of 18 (or 32) to stabilize the catalyst so compatible ligands may be added to complete the coordination shell (step 6). This same process may be applied for selection of a catalyst using any of the first, second or third row transition metals, however, only those with acceptable low positive or negative bonding energies can produce effective catalysts. The approximate, computed, relative bonding energy values may be computed using a semi-empirical algorithm. This computational method indicated that any of the first row transition metal oxygen complexes can produce usable catalysts once the outer coordination shell had been completed with ligands, even though the elements Ti, Mn, Fe, Co, Ni and Cu indicated reasonable bonding energies in a simplified molecular model. Second row transition metal oxygen complexes based on Mo, Ru, Rh, Pd and Ag are indicated to produce active oxidation catalysts. Third row transition metal oxygen complexes are all indicated to produce active oxidation catalysts. In general, preliminary energy values computed for transition metal oxygen complexes are indicated to produce useable catalysts once bonding ligands have been added.
Description of Catalyst Preparation and Hydrocarbon Oxidation
Catalyst preparation has been conducted using nitrogen sparging and nitrogen blanketing to minimize or eliminate air oxidation of the transition metal compounds during preparation. Transition metal catalysts, effective for ambient air oxidation of organic compounds, can be produced by combining transition metal salts in their lowest standard oxidation states. Thus, such transition metal catalysts can be made by reacting alkali metal salts of transition metal(I or II) cyanides with transition metal(I or II) chlorides or bromides in a 1 to 1 or 1 to 2 ratio, or by forming transition metal compounds in a reduced state by similar means where di-, tri- and/or poly-metal compounds result.